<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>透明的单例类的编写优化版</title>
</head>
<body>
<button id="loginBtn">
    登陆
</button>
<script>
 var createLoginLayer = (function () {
     var div;
     return function () {
         if(!div){
             div = document.createElement('div');
             div.innerHTML = '我是登陆浮窗';
             document.body.appendChild(div);
         }
         return div;
     }
 })()
  document.getElementById('loginBtn').onclick = function () {
      var loginLayer = createLoginLayer();
      loginLayer.style.display = 'block';
  }
</script>
</body>
</html>